Communication systems are known to include a central controller, a plurality of communication units, and communication resources. In such systems, the communication resources may be frequencies, pairs of frequencies, TDM slots, or any medium that carries RF (radio frequency) transmissions.
Encrypted, also known as secure, voice and data communication systems are well known. Many of these systems provide secure communications between two or more users by sharing one or more pieces of information between the users, which permits only those users knowing that information to properly decrypt a message. This information includes an encryption key, an encryption algorithm, and in some cases, various initiating information. A message is typically encrypted using a particular encryption algorithm, or technique, using an encryption key that adds extra security into secure transmissions. Examples of encryption algorithms include data encryption standard (DES), digital voice protection (DVP), cipher feedback, and open loop feedback. These encryption algorithms are generally used throughout the secure technology arena.
In secure communication systems, a communication unit has the option of utilizing the security of encrypted transmissions, or transmitting in an unencrypted, or clear, mode. Thus, the central controller, or communication resource allocator, must be equipped to process both clear communication requests and encrypted communication requests. Most communications occur in an encrypted format in secure communication systems. The security of the secure communication system comes from the encryption of communications between two or more communication units. In order for a communication unit to decode such messages, that unit must have both the correct encryption algorithm and the correct encryption key. If either the encryption key or the encryption algorithm are incorrect, a communication cannot be decoded properly.
Because of security issues related with secure communication systems, encryption keys and/or encryption algorithms may be changed within the secure wireless communication system. To maintain security over a longer period of time, secure communication systems regularly change the active system encryption parameters, which include encryption algorithm and encryption key. Such a change may be monthly, daily, or even hourly depending on the nature of security desired. Active system encryption parameters may also be changed as desired, particularly if a communication unit is lost or stolen, thus limiting the time of access an unauthorized user may obtain. When a unit does not have a correct encryption key and encryption algorithm, that unit will not be able to decode any information from a communication that is encrypted using the active system encryption parameters. The unit may, however, continue to communicate in an unencrypted manner.
Because the secure communication system can handle both unencrypted and encrypted communications, it is possible for an unauthorized communication unit to operate on the secure communication system in a clear mode and go undetected. When unauthorized communication units are accessing a communication system, whether a secure or a non-secure system, the efficiency of such systems decreases. Thus, authorized users suffer in slower throughput of their communication requests as a result of unauthorized use of the system.
Present technologies do little to detect unauthorized use of a secure communication system, while a substantial amount of technological effort is placed into ensuring that secure communications remain secure. Therefore, a need exists for a method of detecting unauthorized use of a secure communication system.